64 bit Windows (Vista or XP) will not run 16 bit code. Some 32 bit games have 16 bit installers. These games may run in 64 bit Windows, but won't install. It is sometimes possible to manually install these games. DOS games are not a problem since DOSBox runs easily on 64 bit Vista. Windows 3x can be installed in DOSBox, so Win3x games can be played through DOSBox, too. Then there are the "mixed" bit Win9x games. About the only hope for these games is a virtualizer, such as VitualPC with Win9x installed in it. Keep in mind that most virtualizers don't support parts of DirectX, like D3D, etc. They also tend to have very poor audio.
Though he currently has only a few installers, jafa has made a few XP/Vista installers for some Windows games. You can find his installers at
SquirtTheCat. For DOS based games, check out the
New Sierra Game DOSBox Installers on the Sierra Help Pages that I have been making.